Aircraft wing and method of manufacture



Sept. 27,1949. G. B. RHEINFRANK, JR., ET AL. 2,482,798

AIRCRAFT WING AND METHOD OF MANUFACTURE Filed Feb. 27, 194e v 9 sheets-sheet 1 Sept 27, 1949 G. B. RHEINFRANK, JR., ET AL 2,482,798

Sept. 27, 1949. G. B. RHEINFRANK, JR., ETAL 2,482,798

AIRCRAFT WING AND METHOD OF MANUFACTURE 9 Sheets-Sheet 3 Filed Feb, 27, v1946 Sept. 27, 1949.L G. B'. RHEINFRANK, JR., ETAL 2,482,798

AIRCRAFT WING AND METHOD OF MANUFACTURE Filed Feb. 27, 1946 9 Sheets-Sheet 4 Il I. IIII Il AQW Sept 27, 1949- G. B. RHEINFRANK, JR., ETAL 2,482,798

AIRCRAFT WING AND lVlr-F'ICD` OF MANUFACTURE Filed Feb. 27.' 194e 9 sheets-sheet 5 9 sheets-sheet 6 INVENToRs 7 5 W a P a G. B. RHEINFRANK, JR.

AIRCRAFT WING AND METHOD OF MANUFACTURE Sept. 27, 1949.

Filed Feb. 27, 1946 Sept 27, 1949 G. B. RHEINFRANK, JR., ET AL 2,482,798

AIRCRAFT WING AND METHOD OF lVUIUJI-'ACTURB:

Filed Feb. 27, 1946 9 Sheets-Sheet 7 iElC-l Sept. 27, 1949- G. B. RHEINFRANK, JR., ET AL AIRCRAFT WING AND METHOD OF MANUFACTURE 9 Sheets-Sheet 8 Filed Feb. 27, 1946 v IN VEN TOR 650565 EA/f//VFEH/VA/ JE,

Sept. 27, 1949. G. B. RHEINFRANK, JR., ET AL 2,482,798

AIRCRAFT WING AND METHOD OF MANUFCTURE Filed Feb. 27, 1946 9 Sheets-5h69?, 9

Patented Sept. 27, v1949 i MANUFACTURE George B. Rheinfrank, Jr., Perrysburg, Ohio, and

Wayne A. Norman, Dubuque, Iowa l Application February 2,7, 1946,'Sierial No. 650,592v

18 Claims.

(Granted under the act amended April 30, 192,78*;379 0. Gr. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes withoutthe payment to us of any royalty thereon.

The present invention relates to Va novel air- 5 craft wing structure and to a method of making the wing. Y

In the past aircraft Wing constructions have usually been classified in three main groups, as follows: wood or metal framing covered with a woven fabric. Each type `of wing possesses its own peculiarities and drawbacks,v as well as special fields of use. In the all metal or all wood constructions the outer skin is generally relied on l5 to carry considerable portionsof the load. I-Iowever, in all metal construction the skin has low resistance to bending or twisting moments, even though its tensile strength may be `very high. The metal skin is also not adapted to'resist any 20 large compressive force without vbuckling'. A plywood skin as applied in the. all wood constructions is superior to sheet metal incompression or in bending, at least for equal weight per unit of area, but the best quality Veneer sheets are A25 costly and require expert handling and assembly technique. The third group mentioned above in which a wood or metal frame is covered with a fabric is used mostly in thesmore inexpensive aircraft, and differs from the' other two groupsfzlo in that the fabric or skin is notrequired to lend any strength to the framing, serving only to in-V close the framing andthus present an unbroken airfoil surface.

rIhe principal object of the present invention-gj, is to provide an aircraft` wing embodying a stressed skin of laminated construction and having combined therewith a particular arrangement of structural members adhesively bonded to the laminated skin. wg, t is a related object of the present invention to provide a stressed skin wing structure in which the skin or shellV comprises a low density core faced on each side with a plurality of layers of cloth or fabric impregnated withv a low-pressureqlg, thermosetting resin and in which the layers are bonded to .the core and toeach other by means 'of the fabric impregnating resin.

Another important object ofthe invention is to provide a laminated wing structure of the: 5o stressed skin or monocoque type which will combine advantages of all. metal and all wood constructions, and at the. sameV timeprovide a wing which will be adapted forquantity production at comparatively low cost..A es

(1) all metal, (2) all wood, and (3) l0' of `March 3, 71883', as

Ancillary to the abovestated objects it is an Vobject of the invention to provide a novel method of' making a stressed skin Wing of laminated construction having spaced stiff'eners associated with-the skin and having spar retaining means .forms improvements on and av continuation of developments reported in Modern Plastics of May 1944 under the rtitles Development of glassreinforced low-pressure. plastics for aircraft V(pages 39 to 93) by Colonel Paul-H. Kemmer-and 'of George B. Rheinfrank, Serial No. 492,309 filed June D25, 1943, now Patent No'. 2,414,125.

In the present case the wing structure makes use of a laminated material similar to that disclosed in the prior publications and'application but the invention is concerned with making it feasible to use the material in a wing construction, by providing meansto combine the laminated material with laminated elements adapted to support and adhesively retain a plurality of reinforcing members within a hollow wing. The invention also contemplates the use of a laminated construction for the. reinforcing members, and further contemplates means to rigidly attach the completed wing to the aircraft.

The'above and other objects of the invention will 4become apparent` uponfreading the following. detailed description yin conjunction with the drawings, in which: Y

Fig. 1 is a bottom plan View of the completed wing.v structure ofthe present invention.

Fig. 2 is a perspective View of the assembled wing, the upper skin being mostly cut away to sho-w the interior structuralr arrangement.

Fig. 3 is a perspective view of the wing shells in spaced relation but with the upper shell being lowered into assembled relation. with respect to the lower shell.

Fig. fl is a plan View of the laminated skin forming the lower or outer side of the lower wing shell.

landing gear supporting flanges carried by the upper wing shell interiorly of the wing.

Figs. 11, 12 and 13 are cross sectional detail views taken on lines |||I, l'2-l2 and l3-l3 of Fig. 1.

Fig. 14 is a cross sectional view showing the manner of assembling a wall structure similar to that forming the upper and lower wing shells.

Figs. 15, 16 and 17 are cross sectional Views of one wing shell taken across a spar'connection and showing the shell in three stages of manufacture.

Figs. 18 and 19 are cross sectional views of joint details taken on lines l8--I8 and IQ-l 9 of Fig. 1.

Fig, 20 is a fragmentary perspective view of an upper portion of the wing adjacent the wing root to show the wing attaching means.

The aircraft wing of the present invention comprises an upper laminated shell and a lower laminated shell each reinforced by ribs and of complementary shape for joining at their marginal edges to form a complete hollow wing. The two shells are also joined by spars or stringere extending longitudinally of the wing. Noting Fig. 3 the lower shell is designated I, the upper shell is 2 and the shells are braced and held together by lengthwise members or spars, while each shell is reinforced crosswise by ribs associated with each separate shell. These are the m'ain components of the wing and when completely assembled and adhesively bonded combine to form a rigid and unitary wing structure.

Materials of construction The laminated shells forming the walls of the present monocoque wing structure and also the structural members such as spars, ribs and box flanges are in each case built up of two spaced layers of laminated glass cloth adhesively bonded to a core structure. To illustrate the materials and their manner of assembly into a wall or shell structure attention is directed to Fig. 14. The wall structure as here shown may be used to form the spaced wing shells, and includes the lower layer or skin, a, upper layer or skin b and core layer c. The upper and lower layers are each formed of a plurality of glass cloth sheets separately impregnated with a thermosetting resin in syrup form and are laid up in the relation shown with respect to a core layer. The core in this example is made of resin impregnated glass cloth wrapped around strips of cellular cellulose acetate, the strips and skin layers being bonded under heat and pressure after assembly, the wrapped strips forming wall stiffening elements in the completed assembly.

The glass cloth employed is preferably a fine grade made of yarn formed from continuous glass fibers, and in the uncoated state the cloth has a understood that other fabrics may be substituted if desired, as for instance cloth made of fine wire, linen, ramie or cotton fibers or of any known fibers, natural or synthetic, and the finished fabric may be of any suitable weight or grade. Also it may sometimes be desirable to alternate different plys of fabric such as glass cloth and linen, or glass cloth and ramie cloth.

The resin impregnating and bonding material employed may be of any known type of low pressure thermosetting resin preferably setting to a nal hardened stage by heating to a temperature not over 350? F. Examples which may be used `are phenol formaldehyde, urea formaldehyde,

carbamide formaldehyde or any of the heat setting styrene or melamine resins.

The core strips as above described may be formed with any lightweight core material such as cellular cellulose acetate, balsa wood, basswood or cork. Another material available is called cellular glass or honeycomb glass and comprises plastic impregnated glass cloth or fabthickness of only about 0.003 of an inch. It is w ric corrugated and combined with a number of similar sheets in plastic bonded relation. An advantage in the use of cellular cellulose acetate is the possibility of selecting the density to suit the requirements of local stresses. In making the present Wing it is preferred to use a density of about 'l to 8 pounds per cubic foot in this core material.

In making the sandwich-like material of Fig. 14 or any similar structure the number of cloth layers may vary widely, nor can the average number be illustrated unless drawn to much enlarged scale. As the layers and adjacent elements are bonded together the cloth becomes quite hard and stiff, so that the finished material is of boardlike character and takes on a very smooth surface iinish if molded inrcontact with surface members Yhaving a similar finish.

Wing structure Having described the materials employed in the wing and their use in forming a wall or shell, the present wing construction will now be described in detail. As shown in bottom plan view (Fig. l) the present monocoque wing comprises a tapering structure widest at the root section R and having a leading edge L, trailing edge T, and a landing-light recess or box B. The trailing edge is divided lengthwise into two sections each conextensive in length with two adjoining wing bays. The section nearer the root is eventually fitted with a wing flap while the outer section is built to receive an aileron. A number of inspection openings I are provided in the lower wing shell, to give access to cables and wires. The outer free end E is built to receive a wing tip when completed, this added element being indicated at C in Fig. 2. It is noted also that the wing length is usually termed the span, the width at any point being termed the chord.

Referring to Figs. 2 and 3 the Wing structure is shown as comprising a lower shell I and an upper shell 2, which form a complete monocoque wing when assembled with the ribs and spars, as shown best in Fig. 2. Each individual shell includes an outer skin, a core layer and an inner skin assembled in bonded relation. Each of these shells is a composite structure similar to that described above in connection with Fig. 14. In making the lower shell Vl it is noted that flat surfaces predominate because of the cross sectional shape of the airfoil. Therefore the core elements between the skin layers may be in the form of slabs of cellular material wrapped with plastic impregnated fabric, or inserted between the skin sheets without wrapping especially in the outer wing bays where the need for stiffening of the shells is not so imperative. Where the wing shells have curved surfaces the use of narrow core elements, about one inch wide, permits the laminated shell to take on a smoothly curved shape. It should be understood that all the core elements, whether wrapped to form wall stiifening elements or merely in the form of cellular strips or slabs, extend spanwise of the wing except those elements forming rib flanges to be described below. In the preferred construction the core elements are cut to even length between the ribs, although the wing spar flanges which also form shell core material extend through several bays. The use of wrapped core elements or stiiening elements is preferably limited to the shells in a portion of the root bay where stress concentration is high, this portion being indicated in Fig. l by the series of parallel dotted lines. rllhe core elementsin this bay even though only partially wrapped may be in the form of continuous strips extending the full length of the bay. In the outer bays the shell core comprises merely strips and slabs of cellular material bonded to the skins. Whether the material is or cellular cellulose acetate board, wood, or honeycomb glassrthe bond with the skins appears to be very tenacious. This low density llermaterial may be laid up in random lengths if desired but is preferably cut to t between the rib flanges, that is the same length as the respective wing bays.

In each adjacent bay the thickness of the cellular sheet material varies, so that the shell thickness is graduated from a maximum in the root bay to a minimum in the Wing tip bay. In one example a Wing having a chord of seven and a half feet at the root and a span of fifteen and a half feet embodied cellular material cut from sheets which varied in thickness from 0.525 of an inch for the root bay down to 9.3 of an inch in the wing tip bay.

The skin which forms each face of the wing shells is of graduated thickness, with the laminations cut to predetermined outlines in such a way as to provide strength where it ismost needed. This feature is best illustrated by reference to Figs. 4 and 5, showing in plan the lower or outer skin of the lower shell and the upper or outer skin of the upper shell, respectively. Thus the skin of Fig. 4 comprises seven laminations on the outer face covering one whole side of the wing, one lamination thereunder extending to the line Z-Z, two more laminations extending to line Y-Y, live more laminations extending to line X-X, ve more extending to line W-W ve more extending to line V-V and so on to make up the total lamination thicknesses as indicated for each succeeding zone in the drawings. This graduation of thickness is not carried to such an extent in making the inside skins of each wing shell. The general outline is maintained as in Figs. 4 and 5 but after twenty thicknesses of fabric have been attained no further laminations are added, unless the wing loading is exceptionalf ly high. These inside skins are not illustrated in plan since they differ from the outerv skins only in the extent of lamination build-up near the wing root, as noted above. In spite of the numerous laminations indicated in Figs. 4 and 5 the total thicknesses arernot very great when the material is fully compressed and bonded, so that the variation from one zone to the next does not prevent the core layer from becoming well bonded to the skin.

Referring again to Fig. 3 the wing shells will'be seen to carry ribs 3 to 6 and l I'to I4, and also the spar supporting channels 'l to lil and l5 to I8. The spars 2G to 23 are shown in connection with the upper wing shell and in conformity with good wing design the spars have outwardly tapered webs. According to the present inventive concept the ribs and spars are combined with the wing shells l and 2 in a particular and appropriate manner to result in an erlicient and well integrated structure.

- .Consideringrst the spar constructionY and ar- 6 rangement, reference is made to Fig. 3 to show the main spars 20 and 2l and the auxiliary or false spars 22 and 23. These longitudinal members provide by means of their deep shear webs secured to the wing shells, an internally reinforced wing structure of the monocoque type which will withstand high bending and shear stress. The spar details are best shown in Figs. '7 and 8. Noting Fig. '7 in particular the spar 20 comprises a spar web 20 made up from a core slab 30, core edge element 3| and core covering 32. The core edge element 3i is separately wrapped'with resin impregnated cloth and enclosed with a core slab 30 by means of the fabric covering which is preferably wrapped around the whole core web. Agnn additional core element similar'to element-3| is also included along the oppositelongitudinal edge of the web. The web 20 is adhesively joined to the spar flange elements 33 and 36 situated between the shell skins,

these flange elements being made of wrapped cellular material also. The web supporting channel comprises a lJ-shaped cloth insert 3l of about ten laminations of resin impregnated cloth plus the upstanding cloth layers 38 which form integral continua-tions or web portions of the inside shell skin. With the parts assembled and bonded as shown the spar 20 of I-shaped cross section comprises a web 26] and upper and lower spar flanges forming portions of the wing shells. The anges being located between the wing shell skins are of course bonded thereto, while portions of the skin on each side of the spar are turned up and bonded to the spar web. In the same way the other spars 2l, 22 and 23 are secured to the wing shells, and if desired a series of laminated gussets are set at intervals in the angle between the spars 22 and 23 and the trailing edge portions of upper shell 2. Extending downwardly from the rear edge of the upper wing shell there is a curved fairing sheet 24 of laminated cloth (20'ply) the lower edge of which is bonded to the adjacent spar web. In the` complete wing the aileron is rotatably mounted adjacent to the fairing sheet 24. As shown clearly by Figs. 2 and 3 the upper wing shell extends all the way to the trailing edge at least in the two inner bays, and the pocket formed by the upper shell and the auxiliary spar 22 receives the customary wing ap.

Considering now the ribs or transverse shell reinforcing members which extend chordwise between the spars, it will be noted in Fig. 11 the web 3 of rib 3 is located in contacting alignment with a shell core element Il! flanked on either side by another core. element lll! or 42. These core elements extend across the wing shells between the spar anges at about a right angle to the direction of the spar flanges and the core elements of the shells within the Wing bays. Like other of the shell core elements and like the spar ilanges, the elements lll) to 42 comprise strips of cellular board material wrapped with five to ten laminations of resin impregnated fabric. Until set under proper heat treatment these wrapped strips may be laid on curved surfaces without any diniculty. The same fabric covering is applied to the web 3' of rib 3 and to each similar web. To further secure the web 3 in the position shown, a layer i3 of about ten lamina-tions of fabric is used to enclose the web, with the side edges of the fabric smoothed down and bonded to the inside skin.

Y The core elements lil to 42 extending between the spars form in elect and in fact intercostal rib flanges located between the outer and inner shell-skins, the complete rib comprising the web and Vflanges being of T-shaped cross sectional shape. Thus .in the present wing shells having a substantial core layer, the built-up and spar structures are `easily combined with the shells, since the rib and spar flanges formed of Wrapped cellular material also serve to provide certain portions of the shell core and are held in assembled relation on the wing by the shell skins and other binding sheets to form a unitary wing structure after heat and pressure treatment. Also at the intersection of rib and spar webs it is desirable to place binding sheets formed from small flat squares of laminated `fabric cut half-way in from the middle of one edge, then formed into three planar sections at right angles to each other like the corner of a boX.

The two wing shells are held in assembled complementary relation by the spars and by the leading edge joint shown in detail in Fig. 13. In this joint the upper wing skins are brought down and overlapped on the outside of the lower shell as shown at 41, while the abutting edges of the shells are formed around the wrapped core elements l5 and 56. The shells are not shown as filled with core elements but these elements in the unwrapped .condition are used of course.

To provide a space for the landinglight a box B is built into the leading edge'as shown in Figs. 2 and 3 and is formed of side members 50 and 5I on the lower shell joined by member 222 these all being of laminated fabric over cellular cellulose acetate or other core elements cut to the outlines shown. Similarly the upper half of the box is made from side wall members 53 and Ell joined by wall 55. While this form of light housing is practical, a preferred form of light in the present wing comprises a retractable lamp housing which may extend below the wing and also may be retracted into the wing through an aperture. When retracted the lamp housing fits flush within the aperture, which is provided in the lower wing shell.

Referring to Figs. 1 and l0 the landing gear attaching flanges 60 and 6l will be noted and their manner of attachment to the upper wing shell 2 will be noted in Fig. 10. The flanges are of built up section `comprising a layer of cellular material A52 and a layer -of laminated fabric (60 ply) E3. By the use :of fabric applied as shown in Fig. l these flanges are held in place, after ybeing preformed under heat and pressure.

An attaching means is provided at the root of thawing. and as shown in Figs. 2 and 3 comprises a metallic member 'l0 of angular cross section. The member is formed to the wing contour and the base flange 'lvl is bolted to the wing shells by rst cleaning the cellular material `out of the shell stiffening elements and then applying screws 'I3 through the flange 1l and through shell skins and core wrappings `(see Fig. 20). Nut elements 'M are threaded onto screws i3 as shown. The other member flange l2 is provided with bolt receiving openings to attach the Wing to the aircraft fuselage. Another member l5 of angular cross section is used to hold the spar 20 connected to the fuselage.

Method of manufacture In making up the wing structure as above described the separate shells are each formed in hollow molds having curved inner surfaces like that desired in the finished shells. The outer skin is iirst applied within the mold and built up to the desired thicknesses directly `on the mold surfaces. Then to form the spar supporting channels a plurality ofrnetal bars are wrapped with resin impregnated fabric and mounted on the inner .side of the outer 'skin by several screws passing clear through the bars edgewise, and into the mold. The wrapped bars 80 Will then stand as shown in Fig. 15, after which spar flange elements are laid on each side thereof against the outer skin. If access openings are to be provided in the shell it is necessary to lay in frame members of cellular sheet lmaterial to dei-lne the openings. The next step is that of placing the rib flanges chordwise of the wing shell, these flanges extending between and in abutment with the spar flanges. The core of the shell may then be built up from ystrips and slabs of Icellular material according to the arrangement above described, following which the inside skin is applied and carefully smoothed over the core elements, rib flanges and fabric covered metal inserts located to form the spar supporting flanges. As a nal step the rib elements are set in place on the inner skin and covered with securing strips of laminated fabric, as described in connection with Fig. 1l.

The assembled shell is now ready to be cured under heat and pressure by the use of an air filled bag 8l (see Fi'g. 15), which is confined by the use of a strong non-stretchable fabric covering adapted to be tacked down to the edges lof the mol-d. Fig. 15 is merely a diagrammatic showing of the air bag to show the formation of the spar reinforcing channels, it Ibeing understood that the bag should extend clear across the mold and shell contained therein. For use with a molded wing shell bonded by low pressure thermosetting resin it is preferred to apply pressure to the shell by employing a exible diaphragm, which may be made of a transparent plastic sheet material adapted to be heat-sealed at the edges of the mold. Thus the diaphragm may be made airtight Where it meets the mold edges and is then evacuated to cause the pressure of the atmosphere to be exerted in bonding the shell. With fluid pressure exerted evenly on the shell by the above described or any other means, the mold is then placed in a curing oven and the shell becomes cured and hardened by the application of moderate heat. For numerous resins available at this time the heat need not be very great, temperatures of around 300 F. being ample for most purposes. The pressures applied may be .on the order of two to ten pounds per square inch for many low pressure resins now available.

After forming and curing the two complementary shells, the layers of impregnated fabric over the top edge of the metal inserts 8i] are cut off by means of asharp blade 82 in the manner shown in Fig. 16, to leave a deep channel for reception of spar webs after removal of the metal inserts. If desired the inner skin of each shell may be laid down in sections between the fabric covered metal inserts, and the marginal edges of the skin sections are then brought up against the sides of the wrapped metal inserts to form part of the channel thickness. With this arrangement of the inner skin the assembly is simplified, and also the cutting step to free the metal inserts need onliy apply to the fabric wrapped around the inser s.

To assemble the cured shells'into a hollow wing, the spar vwebs in a preformed and thermoset condition are inserted into the web supporting channels of one wing shell after the liberal application of resinous adhesive thereto. The shells are now brought together at the leading edge portions, which have :been coated heavily with resinous. adhesive, .andsusing thesefportionsfilig.. 13) :as a fulcrumtheiupper.shellis lowered onto the plied to the wing and brought to bear mostly'over .the spars. Theswhole'assembly held together by ,clamps is then cured-maan oven atY proper temfperature to harden theresinous adhesive. If desired/a exible sheetiofmetal may also be strapped in place around the'leading edge to hold the leading edge joint in tight condition while curing.

The wing constructed'in the manner above out- -lined possesses marked advantages over other .types of construction. It has superior strength and durablityas compared toa veneer or plywood constructionand is tougher than the average-all metal wing. Unlike metal structures the present plastic vbonded-wing is not subject to corrosion, Vand resonant effects due to vibration. Furthermore since. .it is not affected by vibration the chancesof fatigue failure are greatly lessened in the present structure. Properly fabricated, the present wing is capable` ofwithstanding high wing loading, is resistant to shock and is not subject to deterioration under dampness, heat, salt air or by contact with. petroleum derivatives. The composite plastic bonded structure disclosed has a very low index of expansion and therefore large variations in temperature do not set up internal stresses.

In manufacturing the wing it is generally preferred' that the wing shells each be preformed and cured before being assembled for final bonding-into a complete hollow wing. However in somecases it maybe desirable, especially in larger Wing sizes, `to make the complete assembly of wing shells-shell reinforcing ribs, spar supporting channelsand -to-a'lso-fassemble the shells in final connectedr relation -with the spar webs in place before applyingA curing heat-and pressure. In soassembling the. shells, the v:molds used in laying up the various elements of each shell vmay abe joined together at their edges with the two shells thus brought intoV assembled relation. To apply molding pressure to. the .wing shells the spaces :interiorly of the wing should be provided with air filled bladders, thepressure of which may be controlled by .air conduitsepassinginto `the Vwing interior from oneorxbothends of the wing. w.Assembling andbonding the whole wing at one time tends toy produce ay stronger and more coherent structure, .and alsofavoids separate curing steps for theshells-and subsequently for-the assembled wing. Y

While .the chordwise shell stiifening ymembers arev termed ribs inthe detailed description. it is to be understood --that theseelements differ from the customary wing ribs in that they do -not formwebs extending from one shell to the other. These ribs arevapplied in the `present double walled structure only to stiffen thewing shells Y and to hold the shells in correct airfoil-shape.

The present invention Ahas been described in conjunction with an aircraft wing of the monocoque typeybut'it is" obvious that the same principles of `construction-maybe applied to other hollow aircraft structures such as elevators,V stabilizers, control'surfaces and also for the aircraft fuselage. In the Llatter -instance the fuselage is made from two similar complementary shells co- 'eXtensive ini-length with the finished fuselage each built Aup -of laminated/material 'assembledand Amolded:according-tol the Iprocedure previously set out in detail. A-seriesjof-shell reinforcing rings are provided infarcuate-sections-and are secured to the-similar shells inthesame-manner as the wing ribspreviouslydescribed. Similarly a series of fuselage stringersfare supported and secured inside eachfshellfportion-by-means of web ysupporting fchanne'ls, as. describedlabove for holding thewing@ spar webs in-:connection 4with the spar flanges. The twoY completedshells are then com- .binedfto produceV .the fuselage .by -j oining stringere situated .along-theshell edges. These adjacentstringere Imay be` bolted together',- in addition to the use fof, resin adhesive at the joint.

The shelf construction-as. disclosed for` use in making the complementary vshells or as described vin conjunction-.withFig. 14s-is adapted for use in aircraft or other struc-tures where a high strength ,lightweight:panel,i=wall,f.loorf or other surfaceformingV member .-is'to Ebe' provided. The wrapped core elementsofk rectangular cross section bonded to resin impregnatediaminated fabric skins provide opposite sets :of parallel faces. One set of faces-of eachcore element. are bonded to the spaced fabric skins 'to form flange-like attaching means, while .the other setof Yfaces are bonded to similar contiguous facesofaadjacent core elements to form afpluralityr-ofwebsextending between the Afabric skins and lying normal thereto. Thus the core elementsA -formv box-sections of-a vlength coextensive withtheskins and-'secured both to the skinsr and to each-other.

The embodimentsofr the .invention herein shown and described are to :be regarded as villustrative only and itis 1tube understoodthat the invention is susceptible to variations, modifications and changes within/the scope of theappended claims.

1. Innansairplanewing construction of airfoil cross section'rhaving.complementary upper :and lower surfacesgiandfhaving spar members run- :ningspanwise ofthewingwith rib members extending` transversely f thereof; .the improvement in which-.said 'upper :and lower surfaces form a unitary double v`v-walled f :monocoque shell having the inner iandwouterviwalls thereof formed of a `plurality .of layersfof fabricimpregnated with a thermosetting resin: and :bonded to eachother land to .-anlowzidensity corefmaterial, said spar membershaving thefflan'ges` thereof bonded to the outer walls of the shell 'andthe inner walls of the-shell having integral -upstanding web p0rtionsbonded to lthewebsof the spars.

2. ."Ul'ie structureras'claimedin claim 1, in which .therib 'mem-bersihave intercostal flange elements bonded tofthe outer wall .foffthefshell'and a portion of the :inner wall of vthe-shell forming upstandingrweb'fportions bonded to the webs of the ribs.

3. A monocoque:shellfconstruction for 'aircraft comprising,complementary shells each having a core :of vlow :density: :material1 Afaced Ion each side .with high .strength resin :impregnated fabric bonded to the core to formnner'andiouter `Walls vonieanh shell; spartmembers.y running lengthwise of each-.shell.andihavingfedge flanges bonded to the louter -shellawalls'aand'lto the innershell walls, :and 4saidniiiin'er shell .awallslihavingiintegral upstanding.' webportionsibondedrto thefwebs of `said sparmembers.

4. .Thegstructure-.asclaimedinfclaim 3in which rirb inenfibers` are providedaextendingxbetween the spar-members,saidrribLfmem-bers having :intercostalf yiiangeslbondeditolthe' outer shell wall yand "It tothe inner shell,v wall'pandiportions Ioffsaid'inner shell wall forming upstanding web portions bonded to the webs of the ribs.

5. A monocoque aircraft wing construction comprising complementary load carrying shell portions forming the upper and lower surfaces of the wing, each of said shell -portions including a central core member of low density material faced on each side with -a plurality of layers `of high strength fabric impregnated and bonded to each other and to the core with a thermosetting resin, and stiffening elements in each shell comprising strips of core material rectangular in cross section covered throughout their length with a plurality of layers of high strength synthetic resin impregnated fabric and bonded on opposite sides to the facings of the shell and the other sides extending substantially norm-al to the facings of the s-hell to function as bracing struts.

6. The structure as claimed in claim 5, in which a plurality of said stiffening elements are arranged in parallel relation extending spanwise of the wing in each of said shell portions to resist bending moments and certain of said last named elements extending from the root substantially rto the til) section of the win-g and `others of said stiening elements extending spanwise only in the regions subjected to high bending moments.

7. The structure as claimed in claim 5, in which certain of said stilfening elements extend generally spanwise of the Wing in each of said shell elements and other of said stiffening elements extend chordwise of the wing, and interconnected shear webs extending spanwise and chordwise of the wing and bonded to said stiffening elements to brace the shell structure against shear and torsional deflections.

8. The structure as claimed in claim 5, in which a pair of said stiffening elements are disposed in parallel planes in said shell members in spaced relation, a channel member having upstanding leg portions positioned in the space between each of said spaced pairs of elements with the bottom of the channel bonded to the outer facing of the `shell and the legs of the channel extending beyond the plane of the inner facing of the shell and the inner facing of the shell having upstanding web portions bonded to the legs of the channel to form integral parts thereof, and `a shear web positioned within said channels and extending therebetween and bonded to the sides and bottoms of said channels.

9. The structure -as claimed in claim 5, in which certain of said stiifening elements are arranged in related pairs in each yof said shell portions, the elements of each pair being spaced apart ,to receive a stiifening channel member of resin impregnated fabric and bonded to the facing material and to the sides of the stiffening elements and the channel having the leg portions thereof extending beyond the plane of the inner facing material and the latter having upstanding web portions bonded to the legs of the channel to form an integral part thereof, and stiifening webs secured in the channels.

10. A stressed skin construction for aircraft comprising a panel having a core of low density material and high strength facing plies on opposite sides of the core, the facing material comprising =a plurality of layers of high strength fabric impregnated and bonded to each other and to the core with a thermosetting synthetic resin adhesive and means for stiffening the panel against forces acting normal to the facing including a plurality of Webs of resin impregnated fabric extending between the facing plies and having ange portions bonded to 'the'respectiveffacing plies and the' websbeing bonded to the core material.

11. In a monocoque shell construction for aircraft including complementary shell portions each comprising a core member of low density material faced on each side with high strength fabric material impregnated with resin and bonded to the core, the improved connection between said complementary shell portions comprising a stiffening element bonded to the core material at a, terminal edge thereof and the facing material on each shell covering the exposed portions of the stiffening elements associated therewith and the facing material on each shell being bonded together to form a flap extending beyond the stiffening element, the ap on one shell being substantially in the plane of the facing material on the outer surface thereof and the flap on the other shell portion being substantially in the plane of the facing material on the inner side thereof, said shells being arranged with the said stiifening elements in parallel abutting relation and adhesively secured together and the flaps on each shell portion being bonded to the facing material on the opposite shell.

12. In a monocoque wing construction for aircraft including complementary shell portions each comprising a core faced on each side with high strength resin impregnated fabric bonded to the core to form inner and outer walls on each shell, the improvement comprising a plurality of stiifening elements extending spanwise of the wing and forming the portion of said core in the region of the wing root, each of said elements comprising a strip of low density material covered with high strength resin impregnated fabric, portions of said elements being hollowed out at the root end of said wing, the outer walls of each shell and the contiguous portions of the high strength fabric of said stiifening elements being apertured adjacent said wing root to receive fastening elements for mounting said Wing on the aircraft.

`13. A method of making a monocoque stressed skin shell section for aircraft comprising the steps of providing a mold corresponding to the desired external contour of the shell, laying up a plurality of layers of synthetic resin coated fabric on the mold surface to form an outer face, wrapping strips of low density core material with resin coated fabric to form stiffening elements with certain of said stiffening elements being arranged in parallel spaced relation to form flange members, covering insert forms with resin coated fabric and positioning the same in the space between said flange members, applying a low density core material to the uncovered portions of the material of the outer face, applying an inner skin of a plurality of layers of synthetic resin coated high strength fabric over the core material, stiifening elements and insert forms, applying curing heat and pressure to the assembly, and trimming the molded material from the tops of the inserts to permit the removal of the same.

14. A method of constructing a composite braced structural shell for aircraft consisting of providing a mold having a surface conforming to the contour of one of the surfaces of the shell, laying thermosetting synthetic resin coated layers of fabric on the mold surface with the number of layers decreasing from a maximum to a minimum along one axis of the shell to form a shell face, applying a plurality of stiiener elements covered with synthetic resin coated fabric to the shell face in parallel abutting relation, certain of said stiifener elements extending beyond the plane of the other of said elements to form webs, applying low density core material to the shell face over the areas not in contact with the stiffener elements, draping a plurality of layers of synthetic resin coated fabric over the assembly to form an inner shell face and applying pressure to the last named layers of fabric to bring them into intimate contact with all of the exposed portions of the stiifener elements, webs and core material, and heating the assembly while under pressure to a curing temperature.

15. A method of making a monocoque wing including complementary wing shells connected to form the completed wing, said method comprising the steps of providing a mold for each shell,

laying up a plurality ofV layers of resin Vimpregnated fabric on the mold surfaces to form outer shell skins, wrapping strips of low density core material with resin impregnated fabric to form shell stiffening elements and placing said elements in contact with said outer shell skins with certain of said stiffening elements being arranged in parallel spaced relation, covering insert forms with resin impregnated fabric and placing the same between said spaced stiffening elements, applying a low density core material to the uncovered portions of the outer shell skins, applying inner shell skins comprising a plurality of layers of resin impregnated fabric over the core material, stiifening elements and insert forms, applying curing heat and pressure to each complementary wing shell, trimming the fabric from the tops of the insert forms to permit removal of the same, inserting resin coated spar webs into the spaces of each shell vacated by the insert forms to connect the shells thereby, providing an adhesive joint at the. leading edge portions of the shells, and applying curing heat and pressure to the assembled shells.

16. A monocoque aircraft Wing comprising a pair of complementary wing shells connected adjacent the leading and trailing edges, each shell having an inner and an outer resin impregnated fabric skin bonded to a core layer, each core layer comprising a plurality of low density striplike core elements in side-by-side relation, at least several of said core elements being covered throughout their length with resin impregnated fabric, one covered core element of each shell forming and defining the leading edge portion thereof, the inner and outer skins of each shell being bonded together beyond the respective leading edge core elements to form double layers of fabric, and the double layers of each wing shell being bonded to one skin surface of the other wing shell.

tions intermediate of the width thereof, said flange and web portions each including a plurality of strips of low density material covered throughout their length and circumference with a plurality of layers of high strength resin impregnated textile fabric to form core elements fixed in sideby-side contacting resin-bonded relation, and means attaching said flange portions to said web portion comprising a plurality of layers of high strength resin impregnated textile fabric bonded by a resinous material to the covering fabric of the cere elements of said ange and web portions.

18. In an airplane wing, a wing spar construction comprising upper and lower spaced flange portions, an upstanding web portion coextensive in lengthV with respect to said flange portions and connected to said flange portions intermediate of the width thereof, said flange and Web portions each including a plurality of low density strips of rectangular cross section covered throughout their length and circumference with a plurality of layers of high strength resin impregnated textile fabric to form core elements fixed in side-by-side contacting resin-bonded relation, facing sheets comprising a plurality of layers of high strength resin impregnated textile fabric bonded to the inner and outer parallel faces of said fiange portions, and means attachingvsaid ange portions to said web portion including upstanding extensions of the facing sheets adjacent to said web portion bonded by a resinous material to the covering fabric of the core elements of said web portion.

GEORGE B. RHEINFRANK, JR. WAYNE A. NORMAN.

REFERENCES CITEDY The following references are of record in the file of this patent:

Y UNITED STATES PATENTS Number Name Date 225,767 Smith Mar. 23, 1880 1,428,714 Schwamb et al. Sept. 12, 1922 1,429,600 Lundin Sept. 19, 1922 1,842,736 Stout Jan. 26, 1932 2,029,048 Atwood Jan. 28, 1936 2,029,214 Atwood Jan. 28, 1936 2,243,432 Moutner May 27, 1941 2,258,134 Clark Oct. 7, 1941 2,273,919 Allward Feb. 24, 1942 2,315,324 Gassner Mar. 30, 1943 2,348,316 Vidal et al. May 9, 1944 2,369,006 Banks Feb. 6, 1945 2,376,653 Boyer May 22, 1945 2,377,846 Dreyfus et al. June 5, 1945 2,445,290 Gouda July 13, 1948 FOREIGN PATENTS Number Country K Date 450,524 Great Britain Apr. 23, 1935 484,305 Great Britain May 3, 1938 519,061 Great Britain Mar. 15, 1940 OTHER REFERENCES Ser. No. 212,074, Dornier (A. P. C.) pub. May ,11, 1943. Y

Modern Plastics May 1944, pages 89-112, 184. 

